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Thread: Fractal wood burning, Lichtenberg figures

  1. #16
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    Quote Originally Posted by Barry McFadden View Post
    It's not high voltage that is the killer... it's high current. You can have high voltage at very low current and not be harmed. No matter what the voltage is, low or high, if there is a high current associated with it that's where the danger is. Current as low as 200mA can be fatal.
    I agree - the high voltage by itself is not necessarily a problem but can enable the current to get into the body, "punch" through the skin even if the normal resistance is high from dry skin, in effect instantly reducing the resistance.

    Some interesting reading: https://www.asc.ohio-state.edu/physi...l_current.html

    An example of high voltage with low current - a small van de graff generator can easily generate 100,000+ volts but the current is only micro-amp. A friend and I built one years ago from a couple of stainless steel mixing bowls. For a party trick he demonstrated 11" sparks off the tip of his tongue. Hold a pin in your fingers and you will get no spark at all since the sharp point starts discharging the sphere at about 3' away. (You can see the spray of electrons at the pin point) But bring the flat of your hand or forearm near the charged sphere and you'll get a surprisingly painful (but harmless) shock at maybe 3-4 inches! But the thing couldn't light a match, let alone burn wood.

  2. #17
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    Quote Originally Posted by Barry McFadden View Post
    It's not high voltage that is the killer... it's high current. You can have high voltage at very low current and not be harmed. No matter what the voltage is, low or high, if there is a high current associated with it that's where the danger is. Current as low as 200mA can be fatal.
    If there's enough current to burn the wood, there's more than enough to cook your guts. I don't know why people pull out the old argument that it isn't the high voltage that kills. If you have a source with sufficient power output to do harm to a human, then high voltage is definitely the killer. It's the high voltage that drives the current up to dangerous levels.

    It's kinda like saying that a fall from a great height won't kill you. It's the sudden stop at the end that does.

  3. #18
    Quote Originally Posted by Frank Pratt View Post
    If there's enough current to burn the wood, there's more than enough to cook your guts. I don't know why people pull out the old argument that it isn't the high voltage that kills. If you have a source with sufficient power output to do harm to a human, then high voltage is definitely the killer. It's the high voltage that drives the current up to dangerous levels.

    It's kinda like saying that a fall from a great height won't kill you. It's the sudden stop at the end that does.
    It's the current that's dangerous in these wood burners not the voltage. Also, high voltage doesn't necessarily drive the current up. Years ago I zapped myself by touching the lead of the picture tube on a tube tv. These leads carry approx. 25000 to 35000 volts but only about 2 mA of current... scared the hell out of me but that's all.....

  4. #19
    Yes, it may be current that kills, not the voltage per se.... But for a given resistance, the current will be proportional to voltage..... (Ohm's law)

    So I would say that higher voltages have the potential to generate higher currents (no puns intended).

    Why else would there be "Danger, High Voltage!" warning signs on the enclosures of devices where high voltages might be present?

    A member of my local turning club does some of this Lichtenberg burning and had the club over to his shop for one of our recent meetings to do a demo. He used a 15KV Neon sign transformer, had leads with insulation rated in excess of the voltage, and wore heavy insulated gloves rated for the voltage as well. I don't recall his footware, but presumably one would want to wear electrically-rated boots or shoes too. After burning a couple pieces, he asked if anyone else wanted to try. No one took him up on the offer. One of the other members of the club is an electrician; he told me he knew people who had died trying this (the implication being he knew them personally...)
    Last edited by Timothy Thorpe Allen; 12-11-2019 at 5:11 AM.

  5. #20
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    Quote Originally Posted by Barry McFadden View Post
    It's the current that's dangerous in these wood burners not the voltage. Also, high voltage doesn't necessarily drive the current up. Years ago I zapped myself by touching the lead of the picture tube on a tube tv. These leads carry approx. 25000 to 35000 volts but only about 2 mA of current... scared the hell out of me but that's all.....
    For a given resistance, higher voltage absolutely will drive the current up as long as the source is capable of delivering the higher current. It's the misconceptions you've presented here that make my argument against untrained people doing this sort of thing.

    And I can relate to your painful TV experience. I did exactly the same thing when I was in high school.

  6. #21
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    What is not clear to me is what exactly is limiting the current for any of these transformers. They don't seem to be complex and current limiting of high voltage is very difficult, therefore I don't feel comfortable with the current limits being discussed. Need to dig into this further.

  7. #22
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    Quote Originally Posted by Pat Barry View Post
    What is not clear to me is what exactly is limiting the current for any of these transformers. They don't seem to be complex and current limiting of high voltage is very difficult, therefore I don't feel comfortable with the current limits being discussed. Need to dig into this further.
    The only current limiting factor is the transformer impedance.

    For a small transformer like that, it may be 10% which would result in a short circuit current of several amperes.

    These transformers are extremely dangerous when not used properly......Regards, Rod

  8. #23
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    Quote Originally Posted by Rod Sheridan View Post
    The only current limiting factor is the transformer impedance.

    For a small transformer like that, it may be 10% which would result in a short circuit current of several amperes.

    These transformers are extremely dangerous when not used properly......Regards, Rod
    This what I've been concerned about. The 'current rating' isn't the maximum current that the transformer can deliver, its the maximum current that it should be designed to be used for.
    I think this is where some of the real danger comes from. People misinterpret that current rating and then compare it to some electrocution hazard data that they don't really understand and then think they comprehend the potential danger. That's why I feel that hand held probes are an accident (potential fatality) waiting to happen, particularly since the users heart is directly in the shortest path for the current to flow from hand to hand.

  9. #24
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    The thing with this particular activity is that in order to be able to burn the fractal design in the wood, the transformer needs to be capable of a dangerous level of current.

  10. #25
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    Quote Originally Posted by Frank Pratt View Post
    The thing with this particular activity is that in order to be able to burn the fractal design in the wood, the transformer needs to be capable of a dangerous level of current.
    Definitely so.

  11. #26
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    Quote Originally Posted by Pat Barry View Post
    Definitely so.
    I was tired of the fractal burned look after the 2nd or 3rd one I saw but other are obviously intrigued by it. Perhaps someone will program a laser engraver to safely engrave a pattern that looks like the fractal design. I don't think the math to randomize the pattern would be that hard.

    JKJ

  12. #27
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    Quote Originally Posted by John K Jordan View Post
    I was tired of the fractal burned look after the 2nd or 3rd one I saw but other are obviously intrigued by it. Perhaps someone will program a laser engraver to safely engrave a pattern that looks like the fractal design. I don't think the math to randomize the pattern would be that hard.

    JKJ
    It could create interesting patterns for sure. Not a replica of the randomness of the electric burns, but certainly safer. The laser program could be made to reproduce the depth and breadth of the burns also. I'd like to see this.

  13. #28
    I personally use a power supply for a neon sign.
    Found that high voltage with less current to be more effective. One would set you back about $80.
    I'm also fortunate enough to come across a length of solid dielectric (non conductive) material to attach a couple probes to.
    Also learned using probes provides a degree of control.
    Even with dielectric probes\wands I use rubber gloves intended for use with high voltage.

    Be safe!

  14. #29
    The point that is missed here (though the OP may just want to play around) is that this is yet another fad that has run its course and coming in on the tail end is likely a waste of time. Being inquisitive is great (as long as it doesnt get you killed). Playing around with it for your own enjoyment is one thing but many events, juried shows, have banned the process.

    Its mind blowing in these days how fast these fad's run their course and are dead. We'll soon be reading endless posts about failed epoxy river tables, the fractal burning lasted months at best. Gah..

  15. #30
    At least part of the reason fads fade away is, people working the fad expect other people think it's really cool and pay for an example... I remember at the fair one year, some guy was making some of the most stunning spray-paint art I've ever seen. He always had a big crowd of people watching him make a painting. When he was done, everyone was 'wow, that was really cool!!' -- but I never saw a single person buy one of his paintings. He would've been better off charging people to watch...
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